Method of controlling intermediate phase cvvt

ABSTRACT

A method of controlling an intermediate phase Continuous Variable Valve Timing (CVVT) includes, in order to determine whether a CVVT operation of an engine can be performed, a voltage of a battery, a pressure of an engine oil, and a temperature of the engine oil are detected, and it is determined whether a CVVT operation can be performed on the basis of the detected voltage of the battery, the detected pressure of the engine oil, and the detected temperature of the engine oil.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of priority to Korean Patent Application No. 10-2015-0080931, filed on Jun. 9, 2015 with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a method of controlling an intermediate phase CVVT and, more specifically, a method of controlling an intermediate phase CVVT, that may expand an operation region of the intermediate phase CVVT and maximize a precise control effect.

BACKGROUND

In general, a Continuous Variable Valve Timing (CVVT) system optimally controls a valve opening/closing timing of an engine according to the number of revolutions of the engine, thereby improving fuel efficiency, reducing exhaust gasses, increasing torque, and improving output. In detail, the CVVT system increases a valve overlap of an intake/exhaust valve of an engine to reduce pumping loss so as to improve fuel efficiency, optimizes the valve overlap according to an engine condition to burn unburned gas by internal Exhaust Gas Recirculation (EGR) so as to reduce an amount of exhaust gasses, and optimizes an intake valve timing according to the engine condition to increase volumetric efficiency so as to improve a low speed torque and improve output.

In recent years, an intermediate phase CVVT system, which improves the existing CVVT system's problems about responsiveness and an operation region limit, has been developed.

FIG. 1 illustrates a comparison between locations of cams of an existing CVVT system and an intermediate phase CVVT system.

As illustrated in FIG. 1, since the intermediate phase CVVT system controls a location of a cam not at a most retarded location (intake) or a most advanced location (exhaust) but at an intermediate location, responsiveness is rapid and a use region of a cam is large, so that fuel efficiency may be improved and an amount of exhaust gasses may be reduced.

In recent years, the intermediate phase CVVT system, which may replace existing CVVT systems, is used to improve fuel efficiency/performance of a vehicle and reduce an amount of exhaust gasses.

Meanwhile, in a case of the existing CVVT system, a release pressure of a lock pin for locking a cam for opening/closing a valve of an engine is 0.3-0.7 bar. However, since the cam operates by pressure of engine oil, a force for driving the cam cannot be obtained under a condition where the pressure of the engine oil is low. Thus, in order to obtain sufficient oil pressure for driving the cam, a logic is used which determines an elapsed time according to an oil temperature after starting, a temperature of engine oil, a voltage of a battery for driving an oil pump, a temperature of engine cooling water and an intake air temperature condition, among other variables, to indirectly determine whether an oil pressure of the engine reaches sufficient pressure for driving the cam, so as to determine whether a CVVT operation can be performed.

Such an analysis of conditions, for determining whether the CVVT operation can be performed, may be equally applied to the existing intermediate phase CVVT system.

Referring to FIG. 2, in the existing intermediate phase CVVT system, as a previous step for driving a cam for opening/closing a valve of an engine, after a location of the cam is identified, when a voltage of a battery satisfies a condition of a predetermined range, a temperature of engine oil satisfies a condition of a predetermined range, and an elapsed time according to an oil temperature after starting satisfies a predetermined condition, it is determined that an operation condition of the CVVT is satisfied such that the CVVT operation can be controlled.

At this time, when the temperature of the engine oil is equal to or lower than a low setting value, it is determined that engine friction is excessive, so that the CVVT operation is restrained. Further, when the temperature of the engine oil is equal to or higher than a high setting value, it is determined that the oil pressure is reduced due to a decrease in oil viscosity, so that the CVVT operation is restrained. Here, the high setting value is set for each number of revolutions of an engine.

In the existing CVVT system, the cam can be driven when oil pressure reaches about 4 bar or more. Further, in general, about 7 seconds are consumed after starting for generating such an oil pressure (oil pressure of about 4 bar or more).

In contrast, in a case of the existing intermediate phase CVVT system, since driving of advancing/retarding of the CVVT system is controlled through a cam torque, when the pressure of the engine oil reaches a lock-pin releasing pressure (about 0.3-0.7 bar), the CVVT operation can be performed. Further, in general, since about 2 seconds are consumed for generating the oil pressure (the lock-pin releasing pressure) after starting, emission (EM) reduction through the valve overlap can be achieved through the CVVT operation immediately after starting, particularly, at a low temperatures during cold starting.

That is, in the intermediate phase CVVT system, when only a minimum oil pressure condition for releasing a lock-pin (the lock-pin releasing pressure is about 0.3-0.7 bar) is satisfied, CVVT driving can be achieved by the cam torque. Thus, as in a technology applied to the existing CVVT system, when it is determined through an indirect scheme whether the intermediate phase CVVT operation can be performed, the CVVT operation conditions are restrained, and particularly, at an initial time of cold starting, the EM reduction through the CVVT operation significantly decreases.

Further, in a case of the indirect determination scheme, since a margin should be always applied to consider an inadequate condition, the CVVT operation conditions are more limited, and thus, a substantive CVVT operation region is reduced.

Please note the following prior patented documents:

-   -   1. Korean Patent Application Publication No. 2003-0029368 (Apr.         14, 2003)     -   2. Korean Patent No. 10-1448794 (Oct. 1, 2014)     -   3. Korean Patent Application Publication No. 10-2013-0002029         (Jan. 7, 2013)

SUMMARY OF THE DISCLOSURE

The present disclosure has been conceived to solve the above-described problems, and an aspect of the present disclosure is to provide a method of controlling intermediate phase CVVT, which may expand a substantive operable region of CVVT by optimizing an enabling condition for determining whether a CVVT operation of an intermediate phase CVVT engine can be performed.

Accordingly, the present disclosure provides a method of controlling intermediate phase CVVT, wherein, in order to determine whether a CVVT operation of an engine can be performed, a voltage of a battery, pressure of engine oil, and temperature of the engine oil are detected, and it is determined whether a CVVT operation can be performed on the basis of the detected voltage of the battery, the detected pressure of the engine oil, and the detected temperature of the engine oil.

As a previous step for driving a cam for opening/closing a valve of the engine, a location of the cam for opening/closing the valve of the engine is identified, and then the voltage of the battery, the pressure of the engine oil, and the temperature of the engine oil are detected.

According to the present disclosure, when the detected pressure of the engine oil is larger than a predetermined pressure setting value, it is determined that an engine oil pressure condition for a CVVT operation is satisfied, when the detected temperature of the engine oil is larger than a predetermined temperature setting value, an engine oil temperature condition for the CVVT operation is satisfied, when the detected voltage of the battery is a value between a predetermined low setting value and a predetermined high setting vale, a battery voltage condition for the CVVT operation is satisfied, and when all of the battery voltage condition, the engine oil pressure condition, and the engine oil temperature condition are satisfied, it is determined that a condition for driving the cam by the pressure of the engine oil is satisfied.

In accordance with the present disclosure, in an intermediate phase CVVT system, a CVVT operation condition is determined on the basis of an actual pressure of engine oil, so that a margin, which is used in the existing indirect determination scheme, may be reduced and an actual CVVT operation region may be expanded. Further, through precise determination of the operation condition, for EM reduction, particularly, in a low temperature section, the system may rapidly enter a CVVT operation at initial starting, thereby maximizing the EM reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not imitative of the present disclosure, and wherein:

FIG. 1 illustrates a comparison between locations of cams of a CVVT system according to the related art and an intermediate phase CVVT system;

FIG. 2 is a flowchart illustrating a method of controlling an intermediate phase CVVT according to the related art; and

FIG. 3 is a flowchart illustrating a method of controlling an intermediate phase CVVT according to the present disclosure.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter, the present disclosure will be described such that those skilled in the art can easily implement the present disclosure.

As described above, in a case of an operation condition determination control logic of an existing CVVT system, a logic is used which determines an elapsed time according to an oil temperature after starting, a temperature of engine oil, a voltage of a battery for driving an oil pump, a temperature of engine cooling water, an intake air temperature condition, among other possible variables, to indirectly determine whether an oil pressure of an engine reaches sufficient pressure for driving a cam, so as to determine whether a CVVT operation can be performed.

The reason why the logic is configured as described above is that, in the existing CVVT system, the cam for opening/closing a valve of the engine can be driven only when the pressure of the engine oil reaches a sufficient pressure of approximately 4 bar or higher. Since an oil pressure sensor is not used, an actual oil pressure of the engine cannot be identified.

In recent years, a two stage variable oil pump system for variably controlling an oil pressure supplied to the engine is used in order to improve a fuel efficiency of the engine, so that an oil pressure sensor, which replaces the existing oil pressure switch, is applied to the engine.

Although some existing engines do not have a sensor installed therein to directly detect and read oil pressure, recent engines may have an oil pressure sensor installed therein to detect the oil pressure so that an Engine Control Unit (ECU) can obtain information on pressure of engine oil, which is required for control.

Further, in an intermediate phase CVVT system, when only a minimum oil pressure condition for releasing a lock-pin for locking the cam (the lock-pin releasing pressure is about 0.3-0.7 bar) is satisfied, CVVT driving can be achieved by the cam torque. Thus, as in a technology applied to the existing CVVT system, when it is determined in an indirect scheme whether the CVVT operation can be performed, the CVVT operation conditions are limited, and particularly, at an initial time of cold starting, the EM reduction through the CVVT operation significantly decreases.

Further, in a case of the indirect determination scheme, since a margin should be always applied to determine an inadequate condition, the CVVT operation conditions are more limited, and thus, a substantive CVVT operation region is reduced.

Thus, when it is determined whether the CVVT operation can be performed, by directly detecting the pressure of the engine oil through a measured value, the CVVT operation region may be optimized.

Accordingly, in order to determine the operation condition of the intermediate phase CVVT system, the present disclosure directly receives an input of the pressure of the engine oil from the oil pressure sensor mounted to the engine, to reduce a margin which should be applied when the pressure of the engine oil is indirectly determined, so as to enlarge the substantive CVVT operation region.

That is, the present disclosure uses an actual oil pressure condition detected using the oil pressure sensor applied to the engine as an enabling condition which determines whether the CVVT operation can be performed in the intermediate CVVT system, thereby enlarging the CVVT operation region and maximizing a precise control effect.

Here, a method of controlling an intermediate phase CVVT according to the present disclosure will be described with reference to FIG. 3.

As illustrated in FIG. 3, first, as a previous step for driving a cam for opening/closing a valve of an engine, a location of the cam is identified.

Next, a voltage of a battery, pressure of engine oil, and temperature of the engine oil, which are required for driving an oil pump, are detected, and it is determined whether a CVVT operation condition is satisfied on the basis of the voltage of the battery, the pressure of the engine oil, and the temperature of the engine oil which has been detected.

That is, the voltage of the battery, the pressure of the engine oil, and the temperature of the engine oil are detected, and it is determined whether the detected voltage, pressure, and temperature satisfy one or more predetermined conditions.

When the detected voltage of the battery is larger than a predetermined low setting value and smaller than a predetermined high setting value for CVVT driving by a cam torque, the pressure of the engine oil detected by the oil pressure sensor is larger than a predetermined pressure setting value for CVVT driving by the cam torque, and the detected temperature of the engine oil is larger than a predetermined temperature setting value for the CVVT driving by the cam torque, it is then determined that a condition for driving the cam by the pressure of the engine oil is satisfied and the CVVT operation condition is satisfied, such that a CVVT operation can be controlled.

Here, the temperature setting value is set to be a minimum temperature condition in which a CVVT operation failure by engine friction does not occur. Thus, when the temperature of the engine oil is equal to or lower than the temperature setting value, it is determined that the engine fiction is excessive, so that CVVT operation is limited.

For example, the temperature setting value may be set on the basis of a temperature condition required for an actual CVVT operation in a low temperature region.

In this way, the pressure of the engine oil is directly detected using the oil pressure sensor provided to measure the pressure of the engine oil, so that it is unnecessary that an order table in which a setting value for an elapsed time after starting is beforehand set according to oil temperature and an order table in which a high setting value for the oil temperature is beforehand set according to the number of revolutions of an engine are beforehand made in order to determine the CVVT operation condition, unlike the related art. Therefore, there are advantages in that a system load is reduced, a CVVT operation entering time is shortened, and information actually detected by using the oil pressure sensor, rather than by data of the order table made through prior mapping, is used so that the operation condition may be determined more precisely.

In this way, the present disclosure improves the analysis of whether the CVVT operation of the intermediate phase CVVT system can be performed , and precisely determines the operation condition so as to enlarge a substantive CVVT operation region, and particularly, makes a CVVT operation time after cold starting earlier so as to reduce low temperature exhaust gasses and improve fuel efficiency/output.

Hereinabove, the present disclosure has been described. The scope of the present disclosure is not limited to the above description, and includes modifications of those skilled in the art, which is based on a basic concept of the present disclosure defined in the following claims. 

What is claimed is:
 1. A method of controlling an intermediate phase Continuous Variable Valve Timing (CVVT), wherein in order to determine whether a CVVT operation of an engine can be performed, a voltage of a battery, a pressure of an engine oil, and a temperature of the engine oil are detected, and it is determined whether a CVVT operation can be performed on the basis of the detected voltage of the battery, the detected pressure of the engine oil, and the detected temperature of the engine oil.
 2. The method of claim 1, wherein when the detected pressure of the engine oil is larger than a predetermined pressure setting value, it is determined that an engine oil pressure condition for the CVVT operation is satisfied.
 3. The method of claim 1, wherein when the detected temperature of the engine oil is larger than a predetermined temperature setting value, it is determined that an engine oil temperature condition for the CVVT operation is satisfied.
 4. The method of claim 1, wherein when the detected voltage of the battery is a value between a predetermined low setting value and a predetermined high setting value, it is determined that a battery voltage condition for the CVVT operation is satisfied.
 5. The method of claim 1, wherein when all of a battery voltage condition, an engine oil pressure condition, and an engine oil temperature condition are satisfied, it is determined that a condition for driving a cam by the pressure of the engine oil is satisfied.
 6. The method of claim 1, wherein, as a previous step for driving a cam for opening and closing a valve of an engine, a location of the cam is identified, and then the voltage of the battery, the pressure of the engine oil, and the temperature of the engine oil are detected. 